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Which of the following is the MOST secure form of tripl…

Which of the following is the MOST secure form of triple-DES encryption?

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A.
DES-EDE3

B.
DES-EDE1

C.
DES-EEE4

D.
DES-EDE2

Explanation:
DES-EDE3 is the most secure form of triple-DES encryption as it uses three different keys for encryption.
3DES can work in different modes, and the mode chosen dictates the number of keys used and what functions
are carried out:
DES-EEE3: Uses three different keys for encryption, and the data are encrypted, encrypted, encrypted.
DES-EDE3: Uses three different keys for encryption, and the data are encrypted, decrypted, encrypted.
DES-EEE2: The same as DES-EEE3, but uses only two keys, and the first and third encryption processes
use the same key.
DES-EDE2: The same as DES-EDE3, but uses only two keys, and the first and third encryption processes
use the same key.
Incorrect Answers:B: DES-EDE1 uses one encryption key and returns the algorithm (and strength) as DES. It is only provided for
backwards compatibility. This is not the most secure form of triple-DES encryption.
C: DES-EEE4 is not a valid form of 3DES encryption.
D: DES-EDE2 uses only two keys and is not the most secure form of triple-DES encryption.

Harris, Shon, All In One CISSP Exam Guide, 6th Edition, McGraw-Hill, 2013, p. 808


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